The goal of this project is to furhter our understanding of enzyme catalysis at a detailed physical-chemical level. The approach we have chosen is to use subzero temperatures, in conjunction with fluid cryosolvents, to slow the catalytic reaction sufficiently to permit the detection and stabilization of normally transient intermediates. Kinetic and structural characterization of the trapped intermediates can then supply the necessary information for a detailed qualitative and quantitative explanation of the catalytic process. Particular systems being investigated include liver alcohol dehydrogenase, dihydrofolate reductase, carbohydrate hydrolases and ribonuclease.